Problem: In the right triangle shown, $AC = 3$ and $AB = 7$. What is $BC$ ? $A$ $C$ $B$ $3$ $?$ $7$
Answer: We know $a^2 + b^2 = c^2$ We want to find $a$ ; let $b = 3$ and $c = 7$ So $a^2 = c^2 - b^2 = 7^2 - 3^2 = 40$ Then, $a = \sqrt{40}$ Simplifying the radical gives $a = 2\sqrt{10}.$